Product reviews are an area of Ecommerce which has come into a lot of critism lately, especially for fake reviews written by people who have a vested interest. That is why all reviews made by your customers have to be approved and published before they are viewable by your site visitors. Reviews are helpful to your customers because it can highlight the best parts of the product. Bear in mind it also gives you a chance to put right a customer who is not happy, before they tell the world.
Reviews can a great way to convey the product to other visitors, they do sometimes need filtering out the though.